Comcast, Verizon, Time Warner Cable and others may be intentionally degrading broadband performance.

Five major ISPs in the U.S. and one in Europe are intentionally allowing broadband performance to degrade for some customers, communications company Level 3 alleged in a recent company blog post.

Mark Taylor, vice president of content and media for Level 3, discussed the company’s peering agreements with ISPs in the U.S., which “have become legal contracts” as peering has become more critical to performance in the past decade. In some of their peering agreements, the ISPs have refused to increase capacity on ports that have become congested, resulting in “congesting that is permanent, [that] has been in place for well over a year,” Taylor wrote.

“They are deliberately harming the service they deliver to their paying customers,” Taylor wrote. “They are not allowing us to fulfil the requests their customers make for content.”

Taylor also provided an example in Dallas in early April, along with a graph that “shows flat tops for most of each day – the port is congest and cannot accept all of the traffic that is trying to get through.”

“Not only are packets being dropped (the number dropped are on the right), but all those not being dropped are also subject to delay,” Taylor wrote.

Taylor stopped short of identifying these ISPs by name, but Taylor did mention that “[a]ll six are large broadband consumer networks with a dominant or exclusive market share in their local market,” and that they all “happen to rank dead last in customer satisfaction across all industries in the U.S.” BGR’s Zach Epstein pointed out that the American Consumer Satisfaction Index, which Taylor cited as the source for his claims about customer satisfaction, lists Comcast, Time Warner Cable, Charter, Cox Communications, Verizon, and Cablevision among the worst in customer satisfaction.

Taylor also implies that monopolization in the broadband industry contributes to this issue.

“In countries or markets where consumers have multiple Broadband choices (like the UK) there are no congested peers,” he wrote.Cogent accused Verizon of “allowing the peer connections to degrade” as a result of a spike in traffic from an unnamed video content streaming provider, Gigaom reported. The peering issues just happened to emerge after Cogent had established a partnership with Netflix.

This is hardly the first time that ISPs have been accused of deliberately slowing broadband performance. Last June, bandwidth provider

Colin Neagle covers emerging technologies and the startup scene for Network World. Follow him on Twitter @ntwrkwrldneagle and keep up with the Microsoft, Cisco and Open Source community blogs. Colin's email address is cneagle@nww.com.